In present-day merchandising point-of-sale operations, data pertaining to the purchase of a merchandise item is obtained by reading data encoded indicia such as a bar code printed on the merchandised item. In order to standardize the bar codes used in various point-of-sale read out systems, the grocery industry has adopted a uniform product code (UPC) which is in the form of a bar code. Various reading systems have been constructed to read this bar code, including hand-held wands which are moved across the bar code and stationary optical reader systems normally located within a checkout counter and in which the bar code is read when a purchased merchandise item is moved across a window constituting the scanning area of the counter, which movement is a part of the process of loading the item in a baggage cart.
Prior scanning systems have utilized holograms for generating a scanning pattern on a target area through which the object bearing bar code indicia passes. The light reflected from the bar code indicia is used in reading the bar code. One example of this type of scanning system may be found in the commonly owned U.S. Pat. No. 4,224,509, in which a plurality of holograms are mounted on a rotating disk, each of the holograms, producing a single scan line on the target area during one revolution of the disk. In order to increase the number of scan lines, the number of holograms mounted on a disk must be increased, which increases the diameter of the disk and the cost of the system. In commonly owned U.S. Pat. No. 4,333,006, a plurality of holograms are mounted on the rim portion of a rotating disk member in which each of the holograms will generate an individual scan beam having a different focal length and diffraction angle from that of the other holograms on the disk. A second set of holograms mounted on the rotating disk focuses the reflected scan beam at a point at which is located an optical detector. Again, the number of holograms mounted on the disk must be increased to increase the density of the scan pattern which increases the cost of the scanner system. While the above-cited scanning system works well in scanning UPC labels mounted on a flat surface, where the UPC label is truncated so as to be located on a small merchandise item such as a package of gum or is located on a curve surface, the reading efficiency of the above cited scanning systems become unacceptable.
It is therefore a principal object of this invention to provide an improved scanning system for projecting a high density multiple-line pattern which provides an enhanced depth of focus at the target area allowing the reading of a label to take place irrespective of the orientation and size of the label.
It is a further object of this invention to provide a scanning system which is high in reader efficiency while low in cost.